Abstract:

Ionomer particles with an inner area and an outer area are provided. The
outer area has an oxidic matrix with cations selected by observing the
following conditions. Only two different types of cations must be present
that belong to one of the following groups (a) to (d), and these two
types of cations must be selected from two different ones of the groups
(a) to (d): (a) ions of the elements of the second main group and
bivalent ions of the transition elements and the lanthanides; (b) ions of
the elements of the third main group with the exception of boron and
trivalent ions of the transition elements and the lanthanides; (c) ions
of the elements of the fourth main group with exception of carbon and
tetravalent ions of the transition elements and the lanthanides (d) ions
of the elements of the fifth main group, selected from ions of antimony
and bismuth and pentavalent ions of the transition elements. Particles of
the composition ZrO2--Y2O3, ZrO2--Al2O3,
BaToO3, Al6Si2O13 are not contained.

Claims:

1. Ionomer particles with an inner area and an outer area, wherein the
outer area has an oxidic matrix with cations that are selected by
observing the following conditions:only two different types of cations
must be present that belong to one of the following groups (a) to
(d);these two types of cations must be selected from two different ones
of the following groups (a) to (d):(a) ions of the elements of the second
main group as well as bivalent ions of the transition elements and the
lanthanides,(b) ions of the elements of the third main group with the
exception of boron as well as trivalent ions of the transition elements
and the lanthanides,(c) ions of the elements of the fourth main group
with the exception of carbon as well as tetravalent ions of the
transition elements and the lanthanides:(d) ions of the elements of the
fifth main group, selected from ions of antimony and bismuth as well as
pentavalent ions of the transition elements;with the proviso that
particles of the composition ZrO2--Y2O3,
ZrO2--Al2O3, BaTiO.sub.3. Al6Si2O13 are not
contained.

2. Ionomer particles according to claim 1, with the with the proviso that
particles of the composition 3 CaOxSiO2 in as much as they are
produced by application of temperatures above 1,000.degree. C. and/or of
particles of a combination of aluminum oxide or silicon dioxide with an
oxide selected from the oxides of lanthanum, zirconium, and yttrium are
not contained.

3. Ionomer particles according to claim 1, wherein the group (b) comprises
the ions of the elements of the third main group with the exception of
boron and of aluminum as well as trivalent ions of the transition
elements and the lanthanides.

4. Ionomer particles according to claim 1, wherein the group (c) comprises
the ions of the elements of the fourth main group with the exception of
carbon and of silicon as well as tetravalent ions of the transition
elements and the lanthanides.

5. Ionomer particles according to claim 1, wherein the oxidic matrix is
homogeneous or substantially homogeneous.

6. Ionomer particles according to claim 1, with spherical or approximately
spherical shape.

7. Ionomer particles according to claim 1, obtained by use of at least one
of the two cations in dissolved form.

8. Ionomer particles according to claim 1, wherein the inner and outer
areas are identical.

9. Ionomer particles according to claim 1, wherein the composition of the
inner areas differs from that of the outer areas.

10. Ionomer particles according to claim 1, with a homogeneous
distribution of the components in the respective areas.

11. Ionomer particles according to claim 1, with cluster-like areas of the
components in the respective areas.

12. Ionomer particles according to claim 1, wherein the two cation types
are selected from the groups (a) and (b) or from the groups (a) and (c)
or from the groups (b) and (c) or from the groups (a) and (d), wherein
the groups (a) and (b) are especially preferred.

13. Ionomer particles according to claim 9, wherein the inner area is
comprised of silicon dioxide and tin dioxide.

14. Ionomer particle according to claim 12 in which the cations of the
group (a) are calcium ions and/or strontium ions.

15. Ionomer particles according to claim 1, whose outer area is
surface-modified by esterification with carboxylic acid or by
silanization.

16. Method for producing ionomer particles according to claim 1,
comprising the following steps:(i) forming a dispersion, a suspension, a
solution, an emulsion, a gel or a sol, by using(1) two organic compounds
containing one and the other of the two cation types, respectively,
according to claim 1, or(2) an organic compound with one of the cation
types according to claim 1 and an oxide or an inorganic salt of the
second cation(3) two oxides of the two inorganic salts according to claim
1, in a suitable liquid medium(ii) effecting an at least partial
hydrolysis and condensation of the component(s) mentioned under (1) and
optionally an at least substantially complete dissolution of the
components under (2) or (3) so that a homogeneous or substantially
homogeneous matrix results,(iii) generating and optionally separating
spherical or substantially spherical particles in or from the liquid
medium, and(iv) drying the spherical or substantially spherical
particles.

17. Method according to claim 16, furthermore comprising the following
steps: heating the dried particles to at least such a temperature at
which optionally still present organic components of the particles are
removed, but not above 1,000.degree. C., preferably not above 650.degree.
C.

18. Method according to claim 16, wherein the particles are generated by
an aerosol method, in particular spray drying.

19. Method according to claim 16, wherein the dispersion, suspension, the
gel or sol additionally is realized by using oxidic particles whose
diameter is below that of the ionomer particles to be produced,
preferably in a range of 1-10%.

20. Method according to claim 16, additionally comprising the steps:(v)
generating a particle dispersion by careful optionally acid-catalyzed or
base-catalyzed hydrolysis, of a metal alkoxide in an alcoholic solution,
separation of the obtained particles from the suspension optionally
drying of the particles, optionally heating of the particles in order to
remove still present organic material, and using the particles for
obtaining the dispersion, suspension, the gel or the sol according to (i)
of claim 16.

21. Method according to claim 16, wherein the particles are formed by
generating an emulsion, a dispersion, or a suspension whereupon they are
removed from the surrounding solvent or the surrounding solvent is
removed.

22. Kit for producing a cement, comprising ionomer particles according to
claim 1 as well as a matrix curable with the aid of or in the presence of
these ionomer particles.

23. Kit according to claim 22, wherein the matrix is a polymer matrix that
comprises, or is, at least one carboxylic acid, preferably a
polycarboxylic acid or a poly alkene acid.

24. Kit according to claim 22, wherein the polymer matrix is a carboxylic
group-containing, homopolymeric for heteropolymeric matrix system,
preferably one of at least one unsaturated mono-, di-, or higher
polycarboxylic acid or its anhydride, to which are added optionally
hydroxy carboxylic acids, in particular citric acid or tartaric acid.

25. Cement, produced by using a kit according to claim 22.

26. Cement, selected from the group of dental cements, bone cements and
adhesives, comprising ionomer particles according to claim 1.

27. Cement according to claim 27, comprising as a further component a
polymer matrix that comprises or is at least one carboxylic acid
preferably a polycarboxylic acid or a poly alkene acid.

28. Cement according to claim 26, wherein the polymer matrix is a carboxyl
group-containing homopolymeric or heteropolymeric matrix system,
preferably one of at least one unsaturated mono- di-, or higher
polycarboxylic acids or its anhydrides, having added thereto optionally
hydroxy carboxylic acids, in particular citric acid or tartaric acid.

29. Cement according to claim 25, wherein the cement is a dental cement,
bone cement, or adhesive for medical or non-medical purposes.

Description:

[0001]The present invention concerns inorganic or optionally organically
modified particles (ionomer particles) that can be subjected in a
targeted way to leaching of certain cations and that are therefore
suitable for use as an inorganic component in so-called glass ionomer
cements. The invention further relates to a method for producing these
particles as well as their use in ionomer cements.

[0002]The term "ionomer particle" is to be understood in the
aforementioned context as inorganic particles that in combination with a
preferably acid-containing matrix can be used in multiple ways as cements
(self-curing, light-curing etc.). In order for a cement-forming reaction
to take place at all, these particles must be instable in a defined or
targeted way, i.e., in combination with water in the presence of the
partner with which they are to be reacted they must release metal ions
that lead to a curing reaction in the partner substance.

[0003]Classic glass ionomer cements with purely inorganic curing action,
light-curing glass ionomer cements (with additional organic polymerizable
components) and so-called compomers (the term is derived by contraction
of the expressions composite and ionomer and is meant to refer to such
cements in which the carboxyl group is bonded to the same molecule that
also carries a cross-linkable double bond; see e.g. "Glass ionomers, The
Next Generation", Proc. of the 2nd Int. Symp. on Glass Ionomers, 1994,
page 13ff) are often used as filler material in particular in dentistry.
As a partner for curing (cement formation) the aforementioned poly alkene
acids are usually used. Advantages of these materials are: no or hardly
any shrinkage up to an expansion caused by the ionomer reaction as a
result of absorbing water; unproblematic incorporation of fluorides and
phosphates; excellent bonding to the tooth tissue (or also to other body
tissues such as bone) as a result of the acid groups in the matrix,
simple application. The basic structure of the usually glass-like
ionomers is comprised of a ternary system of silicon dioxide/aluminum
oxide/calcium oxide. By melting together these components, particles are
obtained which in the presence of, for example, poly alkene acids undergo
a two-stage reaction. By means of the attack of protons of the poly
alkene acids, calcium ions are first leached from the glass composite
and, in an instable phase or so-called primary curing, they are complexed
by the carboxylate groups of the poly alkene acids. The secondary curing
then leads to a stable phase in which also aluminum cations migrate out
of the glass ionomer. Aluminum polyalkenoates are formed as a result of
hydration of the poly salts.

[0004]Disadvantages of the glass ionomer cements are the strength that is
still too minimal, the high wear, and the insufficient x-ray absorption
that are all caused by the currently employed classic ground glass
ionomer particles.

[0005]The known ionomer particles can be obtained inter alia by co-melting
the respective starting compounds (mainly oxides). The grinding process
to which the melted glass ionomer is subjected in order to obtain the
desired particles however promotes the generation of sharp-edged
non-round particles. In this way, the resulting wear resistance of the
ionomer state is unsatisfactory. The formed particles are heterodisperse
and relatively large and must therefore generally be subjected to a
complex classification process in order to obtain them in at least
somewhat acceptable size distribution. In addition to a high labor
expenditure this means also a high material loss and thus extremely bad
yield. The aluminum silicate matrix is often not homogeneous as a result
of co-melting. For example, embedding of fluorides occurs in the form of
calcium fluoride-rich droplets.

[0006]Other cements for dental purposes that are obtained by grinding,
melting and/or sintering, have also disadvantages. WO 00/071082 discloses
the use of a composition of the formula 3 CaO.SiO2 that is known in
the construction industry as a ceramic material in medicine, wherein the
formula must be strictly observed. This material is also known as
Portland cement. By observing specific grain sizes and grain size
distributions that can be obtained however only by a complex method with
several grinding and firing processes to be performed in an inert gas
atmosphere (argon) as well as intermediate quenching steps and by using
very high temperatures (up to approximately 1,250° C.), this
material according to the aforementioned document is well suited for
specific medical purposes.

[0007]A significant improvement relative to the particles that are ground
and/or fired from glasses or other materials are glass ionomer particles
obtained by way of wet-chemical routes (for example, sol-gel
technologies). For example, WO 00/05182 discloses particles obtained in
this way that have a spherical or approximately spherical shape. These
ionomer particles are either purely inorganic particles but they can also
be organically modified.

[0008]The ionomer particles that are producible according to the
aforementioned WO 00/05182 contain, like "classic" ionomer particles, at
least three cationic components in their outer area, i.e., silicon ions,
ions that can occupy the lattice sites of the silicon by generating a
negative charge excess, for example, aluminum, and ions selected from
those of the elements of the first and second main groups as well as
other elements that can be present in bivalent form and can compensate
the negative charge excess. e.g. calcium. It has been found in this
context that in the ionomer reaction in addition to primary and secondary
curing as described above also the outer shell of the ionomer particles
can be dissolved by proton attack with formation of ortho silicic acid.
This ortho silicic acid condenses in the further course of reaction to
silica gel; a gel layer is formed.

[0009]Further developments in the field of ionomer cements are desirable
primarily because making available dually curable glass ionomer cements
in the long run can lead to a boom for the already existing applications
in the medical field as, for example, dental filling material, bone
cement, and adhesives. For this purpose, inexpensive ionomer particles
that can be produced in a simple way are required.

[0010]The inventors of the present invention have now surprisingly found
that even those particles that do not contain more than two different
cation types that are hardly soluble as salts of poly alkene acids can be
used as ionomer particles in the glass ionomer cement reaction when these
particles are produced by wet chemistry (for example the sol-gel route),
As a result of the wet-chemical preparation, the particles have a larger
and more reactive surface area in comparison to conventionally produced
particles (produced by firing and/or grinding from glasses or other
oxides). Because they must not be melted, in some circumstances they may
provide also improved interlinking with the polymer matrix. In
particular, the inventors have found that a network based on SiO2 is
not required in the inorganic matrix of particles into which, as
disclosed in the prior art, the other components are embedded. The
presence of Si--O portions can even reduce reactivity which is not always
desirable.

[0011]Accordingly, the invention provides ionomer particles with an inner
area and an outer area that are characterized in that the outer area
comprises an oxidic matrix with cations whose selection must observe the
following conditions: [0012]two different types of cations must be
present; [0013]the two types of cations must be selected from two
different ones of the following groups (a) to (e): [0014](a) ions of
elements of the second main group as well as bivalent ions of the
transition elements and the lanthanides, [0015](b) ions of the elements
of the third main group with the exception of boron and optionally
aluminum as well as trivalent ions of the transition elements and of the
lanthanides, [0016](c) ions of the elements of the fourth main group with
exception of carbon and optionally of silicon as well as tetravalent ions
of the transition elements and the lanthanides, [0017](d) ions of the
elements of the fifth main group selected from ions of antimony and
bismuth, [0018]from a third of the afore mentioned groups no further
cations may be present in the oxidic matrix.

[0019]The oxidic matrix is preferably homogeneous or substantially
homogeneous. Excluded from the range of protection for the particles
themselves are however those particles whose oxidic matrix is comprised
of calcium oxide and silicon oxide in a molar ratio of 3:1 or contain
this mixture, at least when the particles are produced starting from
calcium carbonate and finely dispersed silicon dioxide (silica gel) by a
method that requires the application of temperatures above 1,000°
C. These particles are disclosed in WO 00/71082. Excluded are preferably
moreover particles of a combination of aluminum oxide or silicon dioxide
with an oxide selected from oxides of lanthanum, zirconium and yttrium,
optionally also zinc, tantalum, tin, ytterbium, barium, and strontium.
Some of the aforementioned particles are disclosed in U.S. patent
application 2002/002214 A1 as filler material for dental materials.
However, these materials are not designed to be a component of an ionomer
cement. Accordingly, in this document any suggestion is lacking that such
particles could be instable in the presence of suitable matrices.

[0020]The invention provides the possibility of making available or
employing ionomer particles in a substantially easier way than before and
with elimination of at least one component, and thus less expensively,
and with great variety. As a result of the wet-chemical production, for
example, by sol-gel route, the energy costs for the production are also
minimal because no high melting or sintering temperatures must be
employed.

[0021]The ionomer particles according to the invention can be particles
with a (completely or substantially) homogeneous matrix of a mixed oxide
of the two aforementioned ion types that optionally contain particulate
inclusions (for example, fluoride salt(s); phosphate) and/or are
surface-modified. In this case, the inner and the outer areas of the
particles are identical. Alternatively, the particles can be of the
core-shell type. In this case, the matrix surrounds as mentioned above a
core that deviates with regard to its composition from that of the
matrix. The composition of the core is not critical because this part of
the particles does not participate in the ionomer reaction. It can
therefore be selected, for example, for the purpose of imparting to the
particles additional properties such as x-ray opacity or the like. Of
course, these particles can also have particulate inclusions in their
matrix area or can be modified on their exterior as described above for
the homogeneous particles.

[0023]In another also preferred embodiment of the invention the ionomer
particles contain moreover phosphate ions. In addition to their
availability for the purpose of remineralization (biocompatibility), by
means of these ions the cement reactivity can also be affected in an
advantageous way in that, in addition to the standard additives, they
provide a further instrument for adjusting the time periods important for
the application, such as processing time and curing time, and that also
have a positive effect in regard to adhesion to tooth and bone.

[0024]In three independent preferred embodiments of the invention the
oxidic matrix of the particles is formed of a combination of elements of
the groups (a) and (b), the groups (a) and (c), as tell as the groups (b)
and (c). Among these combinations that of the groups (a) and (b) is
especially preferred. Even more preferred are particles that contain
calcium ions.

[0025]The individual inventive particles have preferably a spherical or
approximately spherical shape. Particle mixtures should preferably have a
narrow particle distribution. Their size is usually, but not necessarily,
within a nanometer to micrometer range. The particle size can be adjusted
to e.g. between 5 nm and 50 μm, It is preferred to provide relatively
small particles because they have more surface area. In this way, the
reactivity is increased and thus hardening of the cement is accelerated
or improved. A further advantage of smaller particles is an improved
translucence of the resulting cement. Examples of particle sizes are, for
example, 20 nm to 20 μm or 0.5 μm to 50 μm. The respectively
selected particle size can be realized in this context within a narrow
distribution sector that is significantly below an order of magnitude.
Smaller particles, for example, in the range of 50 nm to 1 or 2 μm are
especially suitable as a tooth filling material. In addition to the
already described advantages, for small particles also a particularly
high proportion of ionomer can be incorporated. In order to provide an
especially high proportion of ionomer in the cement, in a special
embodiment of the invention a mixture of two or three batches of ionomer
particles are provided that, with regard to their defined narrow size
distribution, respectively, have such a size ratio relative to one
another that the smaller particles can fit in the gaps of an imaginary
dense sphere packing of the larger particles and the optionally present
much smaller particles fit in gaps of the resulting packing. This
configuration is also particularly suitable for tooth fillings because a
high ionomer proportion in the cement can be realized and mechanically
demanding dental cements should contain particle contents as high as
possible. The bulk density is a parameter that provides information in
regard to the packing behavior of particles. In this way, it is possible
to determine early on in which way high particle contents can be
obtained. However, in addition to relatively small particles, according
to the invention also larger particles should be made available, be it as
the largest batch of a mixture of sizes, as described above, be it for
utilization of the cements in other medical or non-medical fields (for
example, as bone substance or an adhesive).

[0026]In a preferred embodiment the particles are functionalized on the
surface which promotes the prevention of agglomerate formation.

[0027]In another preferred embodiment the particles are porous. Porous
particles (i.e. particles with pores on the outer surface) have as a
result of the higher number of atoms on the outer surface of the
particles a higher ion release/leaching in the presence of water and thus
an improved glass ionomer reaction. Porous particles however also have
disadvantages: they produce a mechanically less stable cement. Therefore,
the degree of porosity is selected in accordance with the desired
purpose. Moreover, a reduced porosity can be selected when the particles
as a result of the ions used for this purpose are especially reactive,
i.e., can be leached especially well in the ionomer cement.

[0028]The porous glass ionomer particles have preferably a pore volume of
0.001 to 2.0 cm3/g, preferably 0.01 to 1.5 cm3/g, and
especially preferred 0.1 to 1.0 cm3/g. The pores are produced by wet
chemistry in low-temperature processes (sol-gel technology emulsion
processes etc.). Under the wet-chemical reaction conditions clusters or
primary particles of the size 1 to 10 nm are formed first that during the
further course of reaction build a network (gel). Depending on conditions
of after treatment, the porous gel network can be densified or compacted
more or less. For a temperature range of below 500° C. greatly
porous systems result while at temperatures above 800° C. in
general almost non-porous but still generally amorphous glass ionomer
particles are produced. In the temperature range above 1,000° C.
particle systems are obtained that have a glass-like to ceramic
character. By appropriate selection of the temperature for after
treatment the porosity can be adjusted accordingly in the desired way
wherein, in particular, when the temperature is set within a range
between 500° C. to 800° C. transitional forms between
greatly porous and less porous particles are obtained.

[0029]By aerosol methods at high temperatures particles can be produced
that have preferably a minimal to small porosity. At temperatures between
1,000 to 1.600° C. the formation of sinter necks is observed first
followed by "merging" of the individual components. In these
high-temperature processes the pores will disappear almost completely and
dense particles are produced primarily.

[0030]The particles can contain additives in homogeneous form or as
particulate inclusions in the aforementioned matrix. These additives can
be for example provided for increasing the x-ray absorption capability or
a change of color, transparency or reflective index.

[0031]Both particle variants, the homogeneous mixed particles as well as
the particles of the core-shell type can be produced by means of the
sol-gel technology or other wet-chemical routes such as emulsion,
aerosol, inkjet or Stober methods. In this context, the particles of the
core-shell type can be produced more elegantly and less expensively
because it is possible in their case to apply on an optionally very
inexpensive core (e.g. of SiO2) a shell of the mixed oxidic matrix
that is relatively variable with regard to thickness. The thickness of
the shell, depending on the COOH contents of the matrix, can be adjusted.
Preferably, it is at least 1-10 nm, even more preferred at least 10-50 nm
so that in cross-section radially outwardly at least approximately 50,
preferably at least approximately 100 metal atoms M of the existing two
types are present on the core. i.e., the thickness of the shell is thus
at least 50-100 times the radius of an M-O group. An upper limit must not
be observed because, as mentioned above, only the outer atom layers
determine the chemistry of the ionomer particles. Additives as the above
described ones can be present in the core and/or in the shell. This
provides the possibility of combining two additives that are possibly not
really compatible with one another in one type of particles.

[0032]The production of the spherical ionomer particles is realized as
mentioned above particularly by way of the different wet-chemical
methods. In this context, a dispersion containing an organic component is
formed in which a controlled hydrolysis and condensation occur. The
expression "dispersion" is used in this context even though possibly also
true solutions, suspensions or emulsions can be obtained or produced in
certain states of the hydrolytic condensation. Also, sol and gel
formation processes are to be included in this expression (for example;
the disperse phase of a dispersion or emulsions can gel). This term
therefore is to be understood to have a relatively broad meaning. The
dispersion can be transformed in different ways, for example, by the
so-called Stober process or spray drying into spherical particles. As an
organic component at least one compound is employed that is selected from
organic compounds of the cations of the elements listed under (a) to (d).
The expression "organic compound" is to be understood as any
"organometallic" compound that comprises at least one organic component
bonded by oxygen to the metal or a complexed organic component or an
organic component bonded to the metal such that in the presence of water,
aqueous or other solvents or dispersion agents (e.g. alcohols) at least a
partial hydrolysis of this compound will be initiated which optionally
will be started only under the effect of acid or base, whereupon the
compound is subjected to a controlled condensation so that chain
condensates or cross-linked condensates are formed in the "solvent" but
no uncontrolled precipitation reaction occurs (the expression "solvent"
is to be understood of course such that the agent in general will not
provide a true solution of the organic compound or compounds; usually a
suspension, a dispersion, an emulsion, a sol or a gel is formed).
Examples of organic compounds are e.g. oxo complexes such as alcoholates
or carboxylates but also other suitable metal complexes or organometallic
compounds. As needed, both cations of the future spherical particles can
be used in the form of so-called organic compounds.

[0033]When a cation of the elements mentioned under (a) is used as an
organic component, not only, but particularly, the carboxylates and
alcoholates are suitable. Especially preferred are magnesium, calcium,
and strontium acetate and the alcoholates, for example, isopropanolate,
of these elements. Further examples are calcium acetyl acetonate or
calcium oxalate. When instead this cation is not to be employed as an
organic compound, the use in the form of optionally extremely fine
powders of the corresponding inorganic compounds, for example, the
oxides, halogenides (chlorides, fluorides), phosphates or other salts
(e.g. Ca(NO3)2, MgCl2, SnCl2) that are soluble or
insoluble in the selected solvents, is suitable. Because these powders
possibly will not completely dissolve and therefore clusters, for
example, oxide clusters, with primarily one cation type may remain, the
oxidic matrix possibly cannot be entirely homogeneous. It is therefore
also referred to as "substantially homogeneous" The clusters should
advantageously have a diameter of less than 50 nm; in general they will
be smaller than 10 nm.

[0034]The metals among which the cations of the group mentioned under (a)
can be selected, comprise e.g. beryllium, magnesium, calcium, strontium,
and barium but also strontium, tin or zinc (the latter in their bivialent
form). By selecting the suitable cations, specific properties can be
generated in a targeted way, for example, x-ray opacity, reactivity,
optical properties or the like.

[0035]When a cation of the elements mentioned under (b) is to be used as
an organic component, preferably oxo complexes are used for this purpose.
As an oxo complex; e.g. alcoholates, diketonates; and carboxylates are
suitable. As examples of alcoholates ethanolate, secondary and tertiary
butylates, for example, of aluminum, should be mentioned. Examples of
carboxylates are those of oxalic acid or methacrylic acid. Acetates or
acetyl acetonates as well as further complexes with chelate forming
agents are also suitable. When instead this cation is not to be used in
the form of an organic component, the use in the form of optionally
extremely fine powders of the corresponding inorganic compounds, for
example, the oxides, halogenides (chlorides, fluorides), phosphates or
other salts (e.g. AlCl3) that are soluble or insoluble in the
selected solvents, is suitable. Further examples are ethyl aluminum
dichloride, iron(III)fluoride, iron(III)citrate, iron acetyl acetonate.

[0036]The elements that can be used under (b) are preferably those of the
third main group, including gallium, indium and thallium. Also, trivalent
niobium, trivalent tantalum, scandium; yttrium, and rare earth elements
such as lanthanum; cerium, gadolinium, ytterbium are suitable. By
selecting special elements, for example, very heavy elements, certain
properties such as x-ray opacity can be produced. Aluminum is suitable in
this connection only to a limited extent. Depending on the selection of
the second component and the degree of porosity and thus of the
reactivity of aluminum containing particles; their ion release rate can
be so high that not in all cases a drop below a satisfactory safety
spacing relative to the toxicity limit is ensured.

[0038]As already mentioned above; the use of silicon as element of the
group (c) is less beneficial because possibly a reactivity reduction must
be contended with. However if for certain considerations silicon is still
to be used as an element of the group (c); for example, in combination
with another especially reactive partner, and this cation is to be used
in the form of an organic component, there are different possibilities to
incorporate the silicon ions into the ionomer particles. For example,
hydrolyzable silanes or siloxanes can be added to the dispersion, for
example, alkyl and/or alkoxy silanes. In this case, particles with a
homogeneous silicate-containing matrix are obtained. Alternatively, to a
dispersion with compounds of the complexed elements of the group (a),
(b), or (d), for example, a second dispersion of silicon dioxide
particles with very minimal diameter can be added. In this case, the
silicon dioxide forms cluster-like structures within the outer area of
the particles that are being formed that, based on the minimal diameter,
are crosslinked very well with the oxide of the other element.

[0039]Examples of starting compounds for the incorporation of cations of
the group (d) are tantalum(IV)butoxide, tantalum(V)chloride, ammonium
heptafluoro tantalate(V).

[0040]When particles are to produced of two cation types, selected from
silicon, aluminum, and calcium, despite the above-mentioned limitations,
as starting compounds alkoxy silanes, aluminum alcoholates, and calcium
acylate are suitable. In particular, aluminum butylate can be used with
calcium acetate or aluminum butylate or calcium acetate, each in
combination with silicon dioxide.

[0041]When the oxidic matrix of the ionomer particles is to contain
phosphate, it can be added in the form of triethyl ortho phosphate.
Fluoride incorporation can be realized by means of hexafluoro silicic
acid or ammonium fluoride.

[0042]The above-mentioned dispersion, depending on the application, can
have further substances admixed. An example is the incorporation of tin
dioxide particles into a sol containing the aforementioned components. In
this way the spherical particles with an inner area (core) of tin dioxide
can be obtained that ensure e.g. excellent x-ray absorption. The core of
the ionomer particles can be comprised instead also of silicon dioxide.
For this purpose, silicon dioxide particles of a suitable size (for
example, with a diameter of 30-100 nm (for example, for the dental field)
or of 1 to 2 μm) are brought into contact with the dispersion so that
the dispersion can deposit on the outer area about the core of silicon
dioxide. The aforementioned ionomer-reactive modifications are only
listed as examples, Many possible variants can be realized as long as the
ionomer particles in their outer area have the aforementioned
ionomer-reactive components.

[0043]The aforementioned organically modified components for producing the
dispersion can be introduced for example into water and optionally acetic
acid or glacial acetic acid can be added (or introduced into the already
acidified solvent). Also, use of basic solvents is possible.
Alternatively, to the organically modified components, for example, in a
non-aqueous dispersion agent, e.g. alcohol, in a suitable way a quantity
of water and optionally base or acid as a catalyst, which quantity is
sufficient for the required hydrolysis process, can be added. Before or
subsequently, the inorganic substances that optionally are also to be
processed can be incorporated, which inorganic substances optionally are
dissolved or dispersed prior to incorporation. In this environment a
hydrolytic condensation of the organically modified components is
initiated wherein however based on the reaction conditions it must be
taken care that hydroxides or oxides will not precipitated in an
uncontrolled fashion. Instead, transformation into chains and/or a
network in which the existing van-der-Waals bonds are sufficient for
obtaining a stable scaffold beyond the spatial area where the particles
develop (i.e., a dispersion or suspension) or through the entire liquid
(with formation of a sol or gel).

[0044]Based on the above described components a dispersion is formed that
can be transformed subsequently into preferably spherical or
approximately spherical particles or from which such particles can be
separated. This can be realized in different ways known to a person
skilled in the art. With regard to this, reference is being had to the
disclosure of WO 00/05182 in which a plurality of suitable methods with
literature reference are mentioned.

[0045]According to the invention it is possible, for example, by means of
a method based on the Stober process to apply onto different inert
particle cores (for example, SiO2, SnO2 cores) a shell
containing silicon ions that contains additional elements of the group
(a) or the group (b) or optionally also group (d). As cores any
monodisperse spherical seeds produced in any suitable way can be
utilized. Inter alia, commercially available agglomerate-free,
monodisperse spherical SiO2 particles (e.g. Ludox, Fa. DuPont) or
SnO2 particles can be used. Based on the aforementioned Stober
process, also monodisperse spherical SiO2 cores in a size range of
50 to 2,000 nm can be produced that are then provided with a "shell".

[0046]For applying the shell, as starting materials organosilicon
compounds such as alkoxy silanes in combination with compounds of the
group (a) or the group (b) (the latter tvo in organic or inorganic form),
optionally of the group (d) instead, can be used. The organic compounds
or a low-molecular weight condensation product thereof are added, for
example to 1-40% by weight of a solvent, preferably alcohol. This
solution is titrated to the mother dispersion of the cores such that
during the course of the growth process of the particles an
oversaturation concentration that would lead to formation of new
particles is not reached. Since according to this method the organic
compounds are to be hydrolyzed, water is added in a concentration that is
matched to the concentration of the educts. Since the
hydrolysis/condensation reactions proceed under neutral conditions very
slowly, an acidic or alkaline medium is preferred. A pH of 8-9 is
advantageous for a uniform growth of the particles and provides
monodisperse ionomer particles of an almost ideal spherical shape. They
are characterized by a surprisingly fast ionomer reaction.

[0047]An in-situ surface modification is achieved inter alia by adding a
silane, for example, of amino propyl triethoxy silane or methacryl oxy
propyl trimethyl silane, in the form of a 1-100% by weight solution to
the dispersion. As a solvent preferably the same solvent as that of the
dispersion is used, for example, ethanol. Also possible is a subsequent
surface modification of the dried particles. For this purpose, to the
particle powder, suspended in approximately 10% by weight in an organic
solvent, for example, toluene an amount of silane required for
monomolecular occupation is added, optionally a catalyst is added and
optionally the reaction is carried out under reflux.

[0048]Furthermore, it was found that emulsion methods are also well suited
for producing the above described ionomer particles. Suitable are O/W as
well as W/O methods, Preferably, the W/O method is used (see, for
example, EP 0 363 927). The proportion of an aqueous phase is preferably
at approximately 15 to 45 volume %, that of the emulsifying agent
preferably at approximately 1 to 20% by weight. During the course of the
emulsion process, a precipitation or gel formation takes place in the
water droplets that preferably is triggered by a basic pH value
displacement. As starting compounds salts and organic complexes of the
above described elements, preferably nitrates, alcoholates, and acetates,
are suitable as well as dispersions already produced therefrom without
limitation. The obtained ionomer particles have surprisingly a narrow
size distribution that can be significantly below an order of magnitude.

[0049]The afore described liquid can instead also be subjected to an
aerosol treatment, in particular, spray drying. For example, very finely
dispersed SiO2 particles or silicon alkoxides can be mixed with
alcoholates or carboxylates of the cations of the groups a) or b) in
aqueous solution at pH<7. With the aid of suitable jets droplets are
sprayed that have a spherical shape. They can be optionally dried, for
example, at approximately 250° C. until the volatile organic
compounds are removed.

[0050]All methods have in common that the obtained particles after removal
of the solvent or after separation from the solvent can be subjected, if
desired, to pyrolysis and sintering in as much as organic components are
still present (for example, at 400° C. to 600° C.) In this
way, hydrocarbon-free ionomer particles are produced. With a careful
application of higher temperatures starting at approximately 500°
C. into a range of approximately 800° C. the degree of porosity of
the particles can be reduced in a targeted way. Temperatures above
approximately 1,000° C. are often undesirable because the
individual particles will melt irreversibly to an aggregate.

[0051]Depending on the employed starting compounds in the aforementioned
method ionomer particles of different structure are formed. The particles
can have a continuous homogeneous area of calcium silicates, strontium
silicates, aluminum silicates or the like. The ionomer particles can be
comprised exclusively of these structures or can have a discrete inner
area that has a different composition, for example, silicon dioxide, tin
dioxide, a mixture of both, aluminum silicate or the like. In a specific
embodiment the spherical ionomer particles are comprised of an inner area
and several outer areas that are preferably shell-like. They can be
produced, for example, in that the silicon dioxide particles of a
suitable size are coated with a first gel or sol, dried and optionally
pyrolyzed whereupon the resulting particles are coated with a second gel
or sol of a different composition, dried again and optionally pyrolyzed.
At least the outermost gel or sol must have in this context a composition
as described above. Even though in general this may not be required, the
aforementioned spherical ionomer particles according to the invention can
also be conventionally silanized or surface-modified in another way.

[0052]When the ionomers according to the invention are incorporated into
matrix systems, preferably in acid-containing matrix systems, according
to the above described two-step curing process cement-like materials, for
example, composites, cements, compomers are produced. Their properties
can be adjusted in a targeted way, as described, by utilization of
corresponding starting substance, for example, by addition of
x-ray-opaque components or by reaction conditions (for example,
concentration, temperature, pH) with which the diameter of the particles
can be varied. These materials are in particular useful in dentistry (for
example, as a filing material) and in the medical sector (for example, as
a bone cement). Furthermore, materials can be produced with differently
adjusted transparency, color, refractive index.

[0053]The ionomer particles according to the invention can be incorporated
into a variety of different organic or partially organic matrices with
which they undergo a glass ionomer reaction (cement formation), Glass
ionomer cements are formed by the reaction of inorganic glass ionomer
particles with an acid-containing matrix system in the presence of water.
The acid-containing matrix system can be of organic nature and is then
generally a carboxyl-group containing polymer matrix system, for example,
one of one (or several) poly alkene acid(s). The matrix system can be a
homopolymer or a copolymer of unsaturated mono-, di-, or higher
polycarboxylic acids (e.g., mono- di-, or tricarboxylic acids) and their
anhydrides or mixtures thereof. Hydroxy carboxylic acids such as citric
acid or tartaric acid can be added to the acid-containing matrix system.

[0054]As select examples polyacrylic acid, poly itaconic acid, and poly
maleic acid should be mentioned. But other acids such as poly phosphonic
acids of e.g. vinyl phosphonic acid, allyl phosphonic acid, vinyl benzyl
phosphonic acid etc. or poly phosphonic acid esters and poly phosphoric
acid esters are in principle suitable as a matrix. The matrix system can
also be an acid-containing inorganic-organic hybrid polymer (eg. ORMOCER,
trademark of the Fraunhofer-Geselischaft, Munchen). Alternatively or
additionally, the matrix system can also contain polymerizable monomers
that can be transformed by a curing reaction (e.g. UV-induced,
light-induced, redox-induced) into a polymer system. In a special
embodiment, the proportion of these monomers is very high (up to 100%) so
that the glass ionomer reaction is affected by the monomers and the
polymerization conditions. But other preferred acidic matrix systems are
also possible for exampile those with poly phosphonic acids such as poly
(vinyl phosphonic acid), systems that contain additional light-curable
components or matrices that can form with ionomer particles the above
described compomers.

[0055]Well-suited acid-containing matrix system for the glass ionomer
particles of the present invention have preferred molecular weights that,
for example, for polyacrylic acid are at 200 to 200,000, particularly
preferred at 5,000 to 50,000. For other poly acids, the molecular weights
can be optionally calculated accordingly. For molecular weights that are
too great gel formation can result that prevents the further glass
ionomer reaction between the particles and the acid-containing matrix and
impairs the compressive strength of the cement.

[0056]The mixture ratio (mass ratio) of acid to particles is beneficially
at 0.001:1 to 10:1 and preferably between 1:5 and 5:1. When the latter
ratios are surpassed or not reached, in many cases excess proportions of
acid or base can be generated in the cement which, for example, with
regard to desired biocompatibility or the dentin adsorption capability,
can have negative effects.

[0057]As matrix systems with which the ionomer particles according to the
invention are processed to cements, the acidic systems already discussed
above in detail are suitable. They can be made available in aqueous phase
or freeze-dried; in the latter state, water must be of course added for
mixing with the ionomers.

[0058]The glass ionomer reaction is carried out with excess water as
reaction medium. The mixture ratio of water to the glass ionomer
particles and acid-containing matrix is preferably 0.01 to 100,
especially preferred 0.1 to 10. Even though the concrete water contents
in many cases can be critical, precise limits can hardly be provided
because the water contents greatly depends on the composition, particle
size, porosity and specific surface area of the glass ionomer particles.
When the water content is too minimal, the release of ions is too low so
that a satisfactory application and satisfactory mechanical properties
such as compressive strength are not enabled. But water contents that are
too high can also be critical because as a result of ion release that is
too high the formation of loose gel networks may result. Gels, as
explained above, are undesirable especially because of their bad
mechanical properties.

[0059]The reaction between the particles and the acid-containing matrix is
preferably carried out in a normal reactor or in a small shaking device
(e.g. VOCO Mix 10), A reaction in autoclaves is also possible.
Temperature from room temperature to 80° C. are suitable;
preferably, temperatures of 20 to 40° C. are selected.

[0060]When the reaction times are relatively long, accelerators can be
used. Preferably, these are complexing agents, for example, citric acid
or tartaric acid, up to a contents of 15% by weight, preferably up to
approximately 5% by weight. Other additives such as stabilizers,
detergents, dispersion agents, pigments etc. are possible. Moreover,
other fillers, i.e., inactive and active fillers, can be added to the
reactive glass ionomer particles. This is always suitable when a porosity
of the cement that is too high is to be compensated for obtaining
excellent mechanical properties.

[0061]In order to obtain a more precise information in regard to the ions
that are released by the respective glass ionomer particles and thus in
regard to the ions that are available for the glass ionomer reaction with
the respective acid-containing matrix, the ion release must be measured.
Such measurements are carried out in water at constant temperatures and
pH value (eg. 6.5 and 3.2) over a period of 24 hours. The samples taken
at defined intervals are then quantitatively assayed by means of atomic
adsorption spectroscopy or ICP analysis. Ion release values of 0.01 mg/l
to 500 mg/l (values given as metal oxide) after 24 hours have been found
to be very beneficial for the present invention. Release values of
preferably 1 to 100 mg/l and particularly preferred of 10 to 50 mg/l have
been found to be especially valuable. However, ionomer cements are also
suitable whose ion release values are outside of the aforementioned
broader range.

[0062]It should be noted that the ion release depends not only on the
composition and temperature treatment of the ionomer particles but also
greatly on their specific surface area; it is directly proportional
thereto. Accordingly, greatly porous particles have generally higher
release values and compact particles in principle have reduced release
values.

[0063]After curing such systems, novel materials (composites, cement,
compomers) are obtained that, while having a simpler composition and
providing for a simpler as well as less expensive manufacture, have in
comparison to know systems similar or significantly improved properties
(x-ray adsorption, mechanical properties etc.).

[0064]For realizing optionally desired high x-ray opacity for reasons of
biocompatibility primarily barium-poor or barium-free compositions are
preferred. They may contain other heavy elements such as preferably Sr,
Y, Sn and the lanthenoides or especially preferred Zr, Nb, or Ta.

[0065]Examples are provided in the following.

EXAMPLE 1

SiO2/Al2O3 Particles; Weight Ratio 75/25

[0066]At room temperature with stirring, 30 ml water and glacial acetic
acid were added to 7.9 g of aluminum secondary butylate. The resulting
Al-containing solution was added dropwise to a dispersion that was
obtained by dilution of 12.3 g of commercial SiO2 sol (silica sol
Ludox AS40, Du Pont company) with 75 g water and 2 ml glacial acetic
acid. After spray drying at approximately 250° C., a white powder
was obtained that according to REM images is comprised of approximately
spherical particles. Measurements by means of x-ray fluorescence (XRF)
confirmed a ratio of SiO2/Al2O3 that is similar to the
educt ratio. A temperature treatment by continuous heating in a muffle
furnace up to 800° C. was carried out subsequently.

[0067]For determining the cement formation and thus the functionality of
the prepared reactive particles, the particles were mixed with a
commercially available poly carboxylic acid (polyacryic acid, MW 60,000)
dissolved in water or a carboxylic add containing hybrid polymer
(ORMOCER®) resin. Curing of the mixture by ionomer reaction occurred
and was detected by means of FTIR spectroscopy of the COO--Al bond being
formed with the aid of an asymmetric band at approximately 1,593
cm-1.

EXAMPLE 2

SiO2/CaO Particles; Weight Ratio 75/25

[0068]At room temperature with stirring, 20 ml water and 1 ml glacial
acetic acid were added to 4.7 g of calcium acetate. The resulting
Ca-containing solution was added dropwise to a dispersion that was
obtained by dilution of 12.3 g of commercial SiO2 sol (silica sol
Ludox AS40, Grace Davison company) with 75 g water and 2 ml glacial
acetic acid. After spray drying at approximately 250° C., a white
powder was obtained that according to REM images is comprised of
approximately spherical particles. XRF measurements confirmed a ratio of
SiO2/CaO that is similar to the educt ratio. A temperature treatment
by continuous heating in a muffle furnace up to 800° C. was
carried out subsequently. For determining the cement formation and thus
the functionality of the prepared reactive particles, the particles were
mixed with a commercially available poly carboxylic acid (polyacrylic
acid, MW 60,000) dissolved in water or a carboxylic add containing hybrid
polymer (ORMOCER®) resin. Curing of the mixture by ionomer reaction
occurred and was detected by means of FTIR spectroscopy of the COO--Ca
bond being formed with the aid of an asymmetric band at approximately
1,555 cm-1.

EXAMPLE 3

Al2O3/CaO Particles; Weight Ratio 50/50

[0069]At room temperature with stirring, 30 ml water and glacial acetic
acid were added to 7.7 g of aluminum secondary butylate. To this mixture,
at room temperature with vigorous stirring, a solution of 4.5 g calcium
acetate with 20 ml water and 1 ml glacial acetic acid was added with
stirring and subsequently diluted with 50 g water. After spray drying at
approximately 250° C., a white powder was obtained. XRF
measurements confirmed a ratio of Al2O3/CaO that is similar to
the educt ratio. A temperature treatment by continuous heating in a
muffle furnace up to 800° C. was carried out subsequently.

[0070]For determining the cement formation and thus the functionality of
the prepared reactive particles, the particles were mixed with a
commercially available poly carboxylic acid (polyacrylic acid, MW 60,000)
dissolved in water or a carboxylic acid containing hybrid polymer
(ORMOCER®) resin. Curing of the mixture by ionomer reaction occurred
and was detected by means of FTIR spectroscopy of the COO--Ca bond and
the COO--Al bond being formed with the aid of asymmetric bands at
approximately 1556 and 1,594 cm-1.

EXAMPLE 3

Al2O3/SrO Particles; Weight Ratio 50150

[0071]At room temperature with stirring, 30 ml water and glacial acetic
acid were added to 8.0 g of aluminum secondary butylate. To this mixture,
at room temperature with vigorous stirring, a solution of 3.3 g strontium
acetate with 20 ml water and 1 ml glacial acetic acid was added with
stirring and subsequently diluted with 50 g water. After spray drying at
approximately 250° C., a white powder was obtained. XRF
measurements confirmed a ratio of Al2O3/SrO that is similar to
the educt ratio. A temperature treatment by continuous heating in a
muffle furnace up to 800° C. was carried out subsequently.

[0072]For determining the cement formation and thus the functionality of
the prepared reactive particles, the particles were mixed with a
commercially available poly carboxylic acid (polyacrylic acid, MW 60000)
dissolved in water or a carboxylic acid containing hybrid polymer
(ORMOCER®) resin. Curing of the mixture by ionomer reaction occurred
and was detected by means of FTIR spectroscopy of the COO--Sr bond and
the COO--Al bond being formed with the aid of asymmetric bands at
approximately 1556 and 1,590 cm-1.

EXAMPLE 5

SnO2/CaO Particles, Weight Ratio 75/25

[0073]At room temperature with stirring 20 ml water and 1 ml glacial
acetic acid were added to 4.7 g of calcium acetate. The resulting
Ca-containing solution was added dropwise to a dispersion that was
obtained by dilution of 33.3 g of commercial SnO2 sol (15% aqueous
dispersion, Alfa Aesar company) with 20 g water and 2 ml glacial acetic
acid. After spray drying at approximately 240° C., a white powder
was obtained that according to REM images is comprised of approximately
spherical particles. XRF measurements confirmed a ratio of SiO2/CaO
that is similar to the educt ratio. A temperature treatment by continuous
heating in a muffle furnace up to 500° C. was carried out
subsequently. In between the temperature was maintained for a time period
of 30 min at 300° C. The resulting particles have a diameter of
4.7 μm (volume distribution) measured by Fraunhofer diffraction. The
specific surface area measured by N2 sorption according to BET was
121 m2/g.

[0074]For determining the cement formation and thus the functionality of
the prepared reactive particles, the particles were mixed with a
commercially available poly carboxylic acid (polyacrylic acidc, MW
60,000) dissolved in water or a carboxylic acid containing hybrid polymer
(ORMOCER®) resin. Curing of the mixture by ionomer reaction occurred
and was detected by means of FTIR spectroscopy of the COO--Ca bond being
formed with the aid of an asymmetric band at approximately 1,556
cm-1.

EXAMPLE 6

SiO2/CaO Particles; Weight Ratio 75/25; Containing F

[0075]At room temperature with stirring, 20 ml water and 1 ml glacial
acetic acid were added to 4.7 g of calcium acetate. The resulting
Ca-containing solution was added dropwise to a dispersion that was
obtained by dilution of 12.3 g of commercial SiO2 Sol (silica sol
Ludox AS40, Grace Davison company) with 75 g water and 0.5 g hexafluoro
silicic acid. After spray drying at approximately 250° C., a white
powder was obtained that according to REM images is comprised of
approximately spherical particles, XRF measurements confirmed a ratio of
SiO2/CaO that is similar to the educt ratio. A temperature treatment
by continuous heating in a muffle furnace up to 800° C. was
carried out subsequently.

[0076]For determining the cement formation and thus the functionality of
the prepared reactive particles, the particles were mixed with a
commercially available poly carboxylic acid (polyacrylic acid, MW 60,000)
dissolved in ater or a carboxylic acid containing hybrid polymer
(ORMOCER®) resin. Curing of the mixture by ionomer reaction occurred
and was detected by means of FTIR spectroscopy of the COO--Ca bond being
formed with the aid of an asymmetric band at approximately 1,554
cm-1.

EXAMPLE 7

SnO2/CaO Particles; Weight Ratio 75/25

[0077]At room temperature with stirring, 20 ml water and 1 ml glacial
acetic acid were added to 4.7 g of calcium acetate. The resulting
Ca-containing solution was added dropwise to a dispersion that was
obtained by dilution of 33.3 g of commercial SnO2 sol (15% aqueous
dispersion, Alfa Aesar company) with 20 g water and 2 ml glacial acetic
acid. After spray drying at approximately 240° C., a white powder
was obtained that according to REM images is comprised of approximately
spherical particles. XRF measurements confirmed a ratio of SiO2/CaO
that is similar to the educt ratio. A temperature treatment by continuous
heating in a muffle furnace up to 800° C. was carried out
subsequently and was supplemented by a holding time at 300° C. The
resulting particles have a diameter of 4.5 μm (volume distribution)
measured by Fraunhofer diffraction. The specific surface area measured by
N2 sorption according to BET was 76 m2/g.

[0078]For determining the cement formation and thus the functionality of
the prepared reactive particles, the particles were mixed with a
commercially available poly carboxylic acid (polyacrylic acid, MW 60,000)
dissolved in water or a carboxylic acid containing hybrid polymer
(ORMOCER®) resin. Curing of the mixture by ionomer reaction occurred
and was detected by means of FTIR spectroscopy of the COO--Ca bond being
formed with the aid of an asymmetric band at approximately 1,555
cm-1.